A screw device such as a ball screw is known as a mechanical element that converts rotational motion to linear motion, or converts linear motion to rotational motion. A typical screw device includes a screw shaft, a nut, and a plurality of rolling elements disposed between a helical groove of the screw and a helical groove of the nut, which face each other, in such a manner as to be capable of rolling motion. The rolling motion of the rolling element is used to achieve agile motion. Accordingly, the screw device is widely used as a mechanical element for motion conversion between rotational motion and linear motion.
When a screw device of this kind is operated under high load and/or at high speed, the screw device may generate heat due to frictional heat. When the screw device generates heat, there are problems such as that the screw shaft expands to reduce feeding accuracy, the preload to be applied to the rolling element increases due to the difference in temperature between the screw shaft and the nut, and a resin component becomes easy to be broken. An important issue for a screw device used in an environment where heat is generated is to cool the screw device.
Known screw device systems include one having a hollow screw shaft to pass coolant through the hollow space of the screw shaft, and one having a nut with a processed cooling passage to pass coolant through the cooling passage of the nut (see, for example, Patent Literature 1).
Moreover, a motion guide device that guides the movement of, for example, a table of a machine tool is known. The motion guide device includes a guide rail and a block assembled to the guide rail via a plurality of rolling elements such as balls and rollers in such a manner as to be capable of relative movement. The table is driven by a driving device such as a ball screw or linear motor. The movement of the table is guided by the motion guide device. The rolling motion of the rolling elements is used to guide the movement of the table. Accordingly, the agile movement of the table can be achieved.
In order to increase rigidity, preload, that is, the load of the rolling element sandwiched between the guide rail and the block is applied to the motion guide device. Moreover, a seal member is mounted on the block. Hence, friction occurs on the motion guide device. When the motion guide device is operated under high load and/or at high speed, the motion guide device generates heat due to the friction. The heat generation leads to the thermal expansion of the rail and the block, and by extension, a reduction in the feeding accuracy of the table, and the thermal expansion of a component to which the rail and the block are attached. The motion guide device needs to be cooled to move the table with high accuracy.
As known motion guide device cooling systems, Patent Literature 2 discloses one having a groove for cooling water formed in a guide rail of a motion guide device to supply the cooling water along the groove and cool the guide rail. Patent Literature 3 discloses one having a passage for cooling water formed in a block of a motion guide device to supply the cooling water along the passage and cool the block.